Google executive chairman Eric Schmidt on Monday said reports that the US government spied on the Internet giant's data centres were "outrageous" and potentially illegal.

In an interview with the Wall Street Journal during a visit to Hong Kong, the Schmidt said that Google had filed complaints with the National Security Agency, US President Barack Obama, as well as members of the US Congress.

"It's really outrageous that the National Security Agency was looking between the Google data centres if that's true. The steps that the organisation was willing to do without good judgement to pursue its mission and potentially violate people's privacy, it's not OK," Schmidt said.

"The NSA allegedly collected the phone records of 320 million people in order to identify roughly 300 people who might be at risk. It's just bad public policy...and perhaps illegal," he added.

"The Snowden revelations have assisted us in understanding that it's perfectly possible that there are more revelations to come."

A news report said the NSA had tapped into key communications links from Yahoo and Google data centres around the world.